Optical disk and optical disk apparatus

ABSTRACT

An optical disc in a sample servo format applicable to high density recording in which a control track area is formed without reducing format efficiency of a rewritable track area and an optical disc device that can read out control information in a short time with a simple circuit configuration are provided. For this purpose, in the optical disc, a space of a predetermined length where emboss prepits do not exist is arranged for each segment in the control track area, following a data area where control data are recorded by emboss prepits as a clock mark, wobble marks and an address mark.

TECHNICAL FIELD

The present invention relates to an optical disc in a sample servoformat and an optical disc device.

BACKGROUND ART

In recent years, as media to record information optically, an opticaldisc, an optical card, an optical tape and so forth are proposed anddeveloped. Among them, the optical disc is drawing attention as a mediumthat can record and reproduce information in a large capacity and ofhigh density.

As for an optical disc capable of recording and reproduction, amagneto-optical (MO) disc is generally known. With regard to the opticaldisc system for performing recording and reproduction of various data byscanning concentric circular or spiral tracks formed on such an opticaldisc with a laser beam, corresponding to its rotation system, there area ZCLV system, which performs recording and reproduction of data bydividing a recording area into zones including a predetermined number oftracks, reducing the number of revolutions in the optical disc stepwisemoving from an inner circumferential zone to an peripheral zone, alongwith the movement of an optical pickup portion that shifts from theinner circumference to the periphery of the optical disc with anincreased number of sectors per one circle (here, the number ofrevolution in each zone is constant), and allowing the linear velocityover the entire disc circle to be substantially constant, and a ZCAVsystem, which performs recording and reproduction of data byrotationally driving an optical disc with its recording area alsodivided into zones while maintaining a constant angular velocity.

Furthermore, an optical disc and an optical disc device in a continuousservo format, which performs a tracking control etc. by using pre-groupsprovided continuously along tracks, and an optical disc and an opticaldisc device in a sample servo format, which performs a tracking controletc. by using prepits in a servo area scattered on tracks, are known.

As an example of a conventional optical disc in the above-mentionedsample servo format, JP8(1996)-115523A describes an optical disc inwhich media information is recorded by the gray code in data areas ofcontrol tracks located in the vicinity of an inner circumferential endand in the vicinity of a peripheral end, and in a servo area of eachsegment, an identification mark providing information for distinguishingthis segment by the recorded position within the servo area is formedtogether with two wobble pits used for tracking control etc. as threeprepits. Then, an optical disc drive confirms whether the various pitpatterns reproduced from the above-mentioned optical disc match the pitpatterns in the predetermined servo areas, and thus, a rotational phaseof the optical disc is synchronized with the phase of a servo clock. Byusing this servo clock, the position of the above-mentionedidentification mark is read out to identify the segment, and at the sametime, control information is obtained by reading out the mediainformation recorded by the gray code.

Furthermore, as an example of a conventional disc not provided with theprepits as mentioned above but with pre-groups, JP10(1998)-320784Adescribes an optical disc in which a control track mark serving as asynchronization signal for a control track area and control informationrepresenting parameter information of a disc are recorded in the controltrack area by forming wobbles in a guide groove of each track, and aservo synchronization signal serving as a synchronization signal for auser area and address information of this sector are recorded in theuser area etc., and a clock mark is formed in the guide groove.

However, the problem with the optical disc that specifies the servo areaby confirming that the pit patterns reproduced by the optical disc drivematch with each other for the three pits including the identificationmark of different recording positions depending on the identificationinformation of the segment and the two wobble pits, is that redundancyincreases in a rewritable track area, which is a user area enablingwriting.

Furthermore, a drive for this type of optical disc must obtain thecontrol information by synchronizing the rotational phase of the opticaldisc with the phase of the servo clock by detecting whether the pitpatterns match with each other in the servo area, identifying thesegment by reading the position of the above-mentioned identificationmark using this servo clock, and also reading the media informationrecorded by the gray code. Therefore, the circuit configuration fordetecting whether the pit patterns are matched becomes complicated. Atthe same time, it takes time until the servo clock comes to a phaselock, and thus it is difficult to read out the control information in ashort time.

Furthermore, in the case of the above-mentioned optical disc, in whichnot only the wobbles containing the synchronization signals and thecontrol information or the address information independent of each otherbut also the clock mark are formed in the guide groove of the respectivetracks, the optical disc is not only incompatible with the sample servoformat but also difficult to be applied to high density recording bynarrowing the track pitch.

DISCLOSURE OF THE INVENTION

Therefore, it is an object of the present invention to provide anoptical disc in a sample servo format applicable to high densityrecording, in which a control track area is formed without reducingformat efficiency of a rewritable track area, and also to provide anoptical disc device that can read out control information in a shorttime with a simple circuit configuration.

To achieve the above object, an optical disc of the present invention ischaracterized in that a plurality of concentric circular or spiraltracks are formed in a control track area where control data arerecorded, in the vicinity of at least one selected from an innercircumferential end and a peripheral end, and in a rewritable arealocated outside the control track area for recording user data at leastin one direction selected from an inner circumference to a periphery andfrom the periphery to the inner circumference depending on the positionof the control track area, and that a plurality of segments are formedin each track, each segment including a clock area where a clock mark isarranged, a servo area where a pair of wobble marks displaced in innercircumferential and peripheral directions from a center line of a trackand separated by a predetermined distance in a circumferentialdirection, an address area where an address mark is arranged and a dataarea for recording the control data or the user data, wherein the clockmark, the wobble marks and the address mark are formed as prepits of anuneven shape, and, following the data area where the control data arerecorded by the prepits of an uneven shape, a space of a predeterminedlength where the prepits do not exist is arranged for each segment inthe control track area.

According to the optical disc of the present invention, in therewritable track area, the data area following the address area, inwhich prepits of an uneven shape (hereinafter referred to as embossprepits) do not exist and the user data are recorded magneto-optically,functions as a space, and a first emboss prepit in a segment immediatelyafter this space easily can be specified as a clock mark. Furthermore,in the control track area, a first emboss prepit in a segmentimmediately after the space following the data area, where the embossprepits exist and thus the control data are recorded, easily can bespecified as a clock mark.

Therefore, the emboss prepits in the clock area, the servo area and theaddress area of each segment are not required to be arranged in uniquepatterns, and redundancy is not increased. As a result, the formatefficiency in the rewritable track area can be enhanced.

In the optical disc of the present invention, it is preferable that thesame control data are recorded in a plurality of tracks neighboring inthe control track area.

According to this configuration, the emboss prepits of the control dataare arranged identically in the radial direction, so that an opticaldisc device can read out the control data only by performing a focuscontrol, without performing a tracking control of tracing the tracksprecisely. As a result, the readout of the control data can be completedin a short time

Furthermore, in the optical disc of the present invention, it ispreferable that the control data in the control track area are recordedby the run-length-limited code.

According to this configuration, even when the control data to berecorded continuously become either a logic 1 or a logic 0, by codingthe data using the run-length-limited code, the emboss prepits actuallyrecorded as the control data do not continue, and the optical discdevice does not erroneously detect it as a space, so that the clock markcan be detected surely.

Moreover, in the optical disc of the present invention, it is preferablethat the predetermined length of the space is a length exceeding adistance between the servo mark and a first prepit of the control datain the control track area.

According to this configuration, when the predetermined length is alength exceeding a distance between the servo mark and the first prepitof the control data in the control track area, the length of the controldata in each segment can be set variably.

In order to achieve the above object, an optical disc device of thepresent invention is an optical disc device for driving an optical disc,in which a plurality of concentric circular or spiral tracks are formedin a control track area where control data are recorded, in the vicinityof at least one selected from an inner circumferential end and aperipheral end, and in a rewritable area located outside the controltrack area for recording user data at least in one direction selectedfrom an inner circumference to a periphery and from the periphery to theinner circumference depending on the position of the control track area,and a plurality of segments are formed in each track, each segmentincluding a clock area where a clock mark is arranged, a servo areawhere a pair of wobble marks displaced in inner circumferential andperipheral directions from a center line of the track and separated by apredetermined distance in a circumferential direction, an address areawhere an address mark is arranged and a data area for recording thecontrol data or the user data, wherein the clock mark, the wobble marksand the address mark are formed as prepits of an uneven shape, and,following the data area where the control data are recorded by theprepits of an uneven shape, a space of a predetermined length where theprepits do not exist is arranged for each segment in the control trackarea, and the optical disc device is characterized in that the opticaldisc device includes reproduction means for reproducing pit signalscorresponding to the prepits, clock mark detection means for detecting apit signal following a distance of not less than a distancecorresponding to the space length from the pit signals reproduced by thereproduction means as the clock mark, servo clock generating means forgenerating a servo clock synchronized with the clock mark detected bythe clock mark detection means and control data readout means forreading out the control data based on the servo clock.

According to the optical disc device of the present invention, with theuse of the clock mark detection means, in the rewritable track area, areproduced pit signal, which follows a distance after the address areacorresponding to the length of the data area where the emboss prepits donot exist and the user data are recorded magneto-optically, can bedetected as a clock mark, whereas in the control track area, areproduced pit signal, which follows a distance corresponding to thelength of the space following the data area where the emboss prepitsexist and thus the control data are recorded, can be detected as a clockmark. As a result, a servo clock having a phase synchronized with aclock mark, that is, with the rotation of the optical disc, can begenerated easily.

Therefore, for generation of a servo clock, it is no longer necessary asconventionally to arrange the emboss prepits in the clock area, theservo area and the address area of each segment in unique patterns andto achieve a phase synchronization of a servo clock by matching thepatterns of the reproduced pit signals with the unique patterns, so thata pull-in speed of a phase lock can be improved with a simple circuitconfiguration.

It is preferable that the optical disc device of the present inventionfurther includes tracking control means for controlling a center of anoptical beam spot to be emitted on the optical disc to match a centerline of a track, based on the results of the pair of wobble pitsreproduced by the reproduction means and servo control means for settingthe tracking control means in a non-operating state at the time when thecontrol data is read out by the control data readout means, wherein thesame control data are recorded in a plurality of tracks neighboring inthe control track area of the optical disc.

According to this configuration, the emboss prepits of the control dataare arranged identically in the radial direction, so that the opticaldisc device can read out the control data only by performing a focuscontrol, without performing a tracking control of tracing the tracksprecisely. As a result, the readout of the control data can be completedin a short time.

Furthermore, in the optical disc of the present invention, it ispreferable that the control data in the control track area are recordedby the run-length-limited code, and that the control data readout meansincludes decoding means for decoding the control data recorded by therun-length-limited code.

According to this configuration, even when the control data to berecorded continuously become either a logic 1 or a logic 0, by codingthe control data using the run-length-limited code, the emboss prepitsactually recorded as the control data do not continue, and when they arereproduced as pit signals, the clock mark detection means does noterroneously detect it as a distance of not less than a space length, sothat the clock mark can be detected surely.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1(a) is a schematic view showing the structure of a segmentarrangement in a rewritable area of an optical disc according to anembodiment of the present invention.

FIG. 1(b) is a plan view schematically showing the structure of segmentsin an optical disc according to an embodiment of the present invention.

FIG. 1(c) is a schematic view showing the structure of a segmentarrangement in a control area of an optical disc according to anembodiment of the present invention.

FIG. 2 is a waveform chart of control data recorded in the optical discof FIG. 1.

FIG. 3 is a block diagram showing the configuration of an optical discdevice according to an embodiment of the present invention.

FIG. 4 is a detailed block diagram of a clock mark detection circuitshown in FIG. 3.

FIG. 5 is a waveform chart of each part in FIG. 4 matched with thesegment structure.

BEST MODE FOR CARRYING OUT THE INVENTION

In the following, a preferable embodiment of the present invention willbe explained based on the drawings. In addition, an optical disc used inthe embodiment of the present invention is a magneto-optical disc in asample servo format applicable to rotational systems of both the ZCLVsystem and the ZCAV system mentioned above.

FIG. 1(a) to FIG. 1(c) are the structural views of segments in anoptical disc according to an embodiment of the present invention. Asshown in FIG. 1(b), a control track area where control data are recordedis provided in the vicinity of an inner circumferential end of theoptical disc. The control data include, for example, generationinformation of media, vendor information of media, information ofrecording reproduction characteristics of a disc (laser power etc.),format information and so forth. Furthermore, a rewritable track areawhere user data are recorded and reproduced as magneto-optical signalsis provided outside the control track area, covering the optical discfrom the inner circumference to the periphery.

Each of the tracks in the rewritable track area and the control trackarea is divided into 1280 pieces of segments, and the layout of eachsegment is shown in FIG. 1(a) and FIG. 1(c) respectively.

As shown in FIG. 1(a) and FIG. 1(c), each segment includes a clock area,a servo area and an address area. In these areas, information expressedby marks of an uneven shape called pits, prepits or emboss prepits isrecorded in advance. Hereinafter, the terms “pit” and “mark” are usedwith the same meaning. Here, a bit length and a numbering of informationrecord are expressed by the number and the numbering of a servo channelbit (hereinafter referred to as a SCB) by taking one clock cycle of aservo clock as a unit, to be described later. As shown in the drawings,the clock area includes 6 SCB, and the servo area includes 16 SCB, andthe address area includes 6 SCB.

A clock mark formed in the clock area includes one emboss prepit withits center positioned in the center line of a track, and, as will bedescribed later, the clock mark is used for generating a servo clockSCLK in an optical disc device that drives optical discs.

Servo marks formed in the servo area includes a pair of wobble pitswhose centers are displaced in inner circumferential and peripheraldirections from the center line of a track by a half track pitch andwhich are separated by a predetermined distance in the circumferentialdirection, and, as will be described later, the servo marks are used inthe optical disc device that drives optical discs for generating atracking error signal TE, which is a difference between signal levelsobtained from the centers of the two wobble pits.

An address mark formed in the address area includes one emboss prepitwith its center positioned in the center line of a track, and addressinformation of one sector can be obtained from address marks in 80pieces of segments provided either with this emboss prepit (indicatingbit “1”) or without (indicating bit “0”). In other words, although it isnot shown in the drawing, one sector includes 80 segments, and 16sectors are formed in each track.

In addition to the clock area, the servo area and the address area, eachsegment in the rewritable track area includes a data area of 297 SCBwhere user data are recorded and reproduced as magneto-optical signalsand emboss pits do not exist. On the other hand, each segment in thecontrol track area includes a data area of 126 SCB where control dataare recorded as emboss prepits.

Furthermore, each segment in the control track area includes a gap of 6SCB between the address area and the data area. The reason for arrangingthis gap is, in the case where an emboss prepit exists in the addressarea (data “1”) and when pit signals are reproduced by the optical discdevice, to avoid a state in which correct information cannot be obtainedas a result of the reproduced pit signals interfering with an opticalbeam spot focused on both the address mark and the first prepit of thecontrol data.

Moreover, each segment in the control track area includes a space of 165SCB where emboss prepits do not exist, following the data area where thecontrol data are recorded by the emboss prepits. By arranging thisspace, an emboss prepit following a sufficiently long space easily canbe specified as a clock mark of a clock area in the next segment. Thisalso applies to each segment in the rewritable track area, and the dataarea where emboss pits do not exist and the user data are recorded andreproduced as magneto-optical signals can be regarded as theabove-mentioned space, so that an emboss prepit following the data areaeasily can be specified as a clock mark of a clock area in the nextsegment.

As described above, the space length in each segment of the controltrack area was set as 165 SCB, but this space length can be increased ordecreased according to the amount of data required as the control datato be recorded in the data area. However, the space length required forspecifying a clock mark should be larger than a maximum distance amongthe distances between the clock mark, the servo mark, the address markand the first prepit in the data area. In the case of the presentembodiment, the space having a length that is larger than the distancebetween the servo mark and the first prepit in the data area at the timewhen the address mark is “0” (that is, a prepit does not exist) isrequired.

Here, the control data to be recorded in fact have been encoded by therun-length-limited (RLL) code. This is done to exclude the possibilitythat the optical disc device will erroneously detect it as the spacefollowing the data area as mentioned above when a run exists in thecontrol data, that is, when the control data to be recorded continuouslybecome either a logic 1 or a logic 0. In the present embodiment, as theRLL code, the Bi-Phase code that can be decoded easily is used. FIG. 2shows a waveform of the control data modulated by using the Bi-Phasecode. As shown in FIG. 2, one bit of the control data as recordinginformation includes 6 SCB, and the shortest mark of the actuallyrecorded waveform that is modulated by the Bi-Phase code is 3 SCB.

In the present embodiment, the data area of 126 SCB is provided, and 6SCB becomes 1-bit control data by the Bi-Phase code, so that 21-bitcontrol data can be recorded per one segment. Therefore, the controldata per 1 track (1 cycle) become 21 bits×1280=26880 bits. Naturally,when the amount of information required as the control data is smaller,the control data per one segment may be reduced from 21 bits.Furthermore, when a larger amount of information is required, the spacelength following the data area can be reduced to lengthen the data area,but in this case, as described above, the space length is required toexceed the distance between the servo mark and the first prepit of thedata area.

In the present embodiment, exactly the same control data are recorded inthe plurality of tracks neighboring in the control track area. Due tothis configuration, the emboss prepits are arranged identically in theradial direction of the optical disc, so that the optical disc devicethat reproduces this optical disc can read out the control data only byperforming a focus control, without performing a tracking control ofpositioning the center of the optical beam spot in the center line ofthe track precisely. As a result, the readout of the control data can becompleted in a short time.

Next, an optical disc device that records and reproduces user data bydriving the optical disc of the above-mentioned embodiment will beexplained by referring to a magneto-optical disc device.

FIG. 3 is a block diagram showing the configuration of a magneto-opticaldisc device according to an embodiment of the present invention.

In FIG. 3, 1 is a magneto-optical disc, and 2 is a spindle motor forrotating the magneto-optical disc 1. 3 is an optical pickup(reproduction means), which not only focuses a light beam emitted from abuilt-in semiconductor laser 31 onto the magneto-optical disc 1, butalso leads the light beam reflected from the magneto-optical disc 1 to abuilt-in photodetector 32 and outputs electric signals after conversion.

4 is a RF Amp (reproduction means), which amplifies and calculates theoutput signals from the optical pickup 3 for detection of amagneto-optical signal (MO), a pit signal (PIT) and a focus error signal(FE). 5 is a data detection circuit used for decoding the recordedinformation from the magneto-optical signal and transmitting it to anerror-correction encoding/decoding circuit 6. The error-correctionencoding/decoding circuit 6 performs an error-correction decodingprocess for the output signal from the data detection circuit 5 andtransmits the data to an external interface (I/F) 22 via a systemcontroller 21, and with regard to user data input from the external I/F22 via the system controller 21, the error-correction encoding/decodingcircuit 6 performs an error-correction coding process and transmits thedata to a recording coding circuit 7. The recording coding circuit 7converts the signals sent from the error-correction encoding/decodingcircuit 6 into sequences of codes suitable for recording and transmitsthe recorded signals to a magnetic head driver 8. The magnetic headdriver 8 sends a recording current, whose positivity and negativity isreversed according to the recorded signal, to a magnetic head 9, and themagnetic head 9 applies a recording magnetic field reversed by therecording current to the magneto-optical disc 1.

10 is a laser driver, and as will be explained later, the systemcontroller 21 obtains recording laser power and reproduction laser poweras information of recording reproduction characteristics from thecontrol data (CDAT) read out by a Bi-Phase decoder 13 (control datareadout means), and the recording laser power and the reproduction laserpower are set in the laser driver 10 via a servo processor 16. Wheninformation is reproduced, the laser driver 10 performs a d.c. emissionfor the semiconductor laser 31 within the optical pickup 3 with the setreproduction power, and when information is recorded, the laser driver10 performs a pulse emission for the semiconductor laser 31 with the setrecording laser power through a servo clock (SCLK) fed from a PLLcircuit 12 (servo clock generating means).

11 is a clock mark detection circuit (clock mark detection means) fordetecting a clock mark from the pit signal (PIT) sent from the RF Amp 4.The PLL circuit 12 generates a servo clock (SCLK) synchronized with theclock mark detected by the clock mark detection circuit 11. 13 is theBi-Phase decoder, which obtains control information through a Bi-Phasedemodulation of the pit signal sent from the RF Amp 4, when the controldata recorded in the control track area are reproduced. 14 is an addressdetection circuit, which picks an address mark out from the pit signaland decodes the address information. 15 is a tracking error (TE)detection circuit, which picks a pair of wobble marks out from the pitsignal and outputs its difference value as a tracking error signal (TE).

The servo processor 16 regards the focus error signal (FE) sent from theRF Amp 4 or the tracking error signal (TE) sent from the TE detectioncircuit 15 as error information and performs a focus control of theoptical beam by driving an objective lens actuator (not shown) withinthe optical pickup 3 in the direction parallel to the emitted directionof the optical beam via an actuator driver 17 or a tracking control ofthe optical beam by driving the objective lens actuator (trackingcontrol means) in the direction parallel to the radial direction of themagneto-optical disc, also via the actuator driver 17. Furthermore, theservo processor 16 also performs a transposition control of the entireoptical pickup 3 by driving a traverse motor 19 (tracking controlmeans), which shifts the entire optical pickup 3 in the radial direction17 via a traverse driver 18 (tracking control means), and a rotationaldrive of the magneto-optical disc 1 at a constant linear velocity (CLV)or at a constant angular velocity (CAV) by driving the spindle motor 2via a spindle driver 20.

The system controller 21 reads out the control data (CDAT) sent from theBi-Phase decoder 13 and sets, for example, the recording/reproductionlaser power for the laser driver 10 as information of recordingreproduction characteristics, or manages the transmission/reception ofthe user data with the external I/F 22 and the operation of the entiresystem.

Next, the operation of detecting a clock mark by the clock markdetection circuit 11 will be explained by referring to a detailed blockdiagram of the clock mark detection circuit 11 shown in FIG. 4 and alsoto waveform charts of each part shown in FIG. 5.

When the magneto-optical disc 1 rotates a predetermined number ofrevolutions and the pit signal (PIT) is input from the RF Amp 4 to theclock mark detection circuit 11 in the focus-controlled state, a binarycoding circuit 41 converts the pit signal into a binary digital signal(See FIG. 5(d) and FIG. 5(e), an enlarged view of one portion in FIG.5(d)). The binary coded signal (BP) sent from the binary coding circuit41 is input to a clear input of a counter 42. A clock signal (MCLK) alsois input to the counter 42, and the counter 42 is cleared when thebinary coded signal (BP) is a logic 1, and the counter 42 counts theclock signal (MCLK) when the binary coded signal (BP) is a logic 0 (timet0). A count value (QO) sent from the counter 42 is input to one ofinput terminals of a comparator 43, and set data (Ds) corresponding tothe above-mentioned space length is fed into the other input terminal ofthe comparator 43. When the count value (QO) exceeds the set data (Ds)(time t1), the comparator 43 outputs a logic 1. An output signal (CO)from the comparator 43 (CO) is fed into one of the input terminals of anAND circuit 44, and the binary coded signal (BP) is fed into the otherinput terminal. Therefore, as shown in FIG. 5, at the output of the ANDcircuit 44, the position of a first prepit in a segment 1 following thespace of a segment 0 will be detected (time t2).

In this way, when the prepit appearing after the space of apredetermined length is once detected, this prepit is used as acandidate for a clock mark (CM), and a detection window (FIG. 5 (b)) isarranged before and after a timing when the next clock mark shows up.When the prepit is detected in the detection window successively for apredetermined number of times, the system controller 21 judges that thedetection of the clock mark is already established.

Here, the clock signal MCLK used for the detection of a clock mark maybe a clock signal of a fixed frequency obtained from a crystaloscillator or the like. The set data (Ds) of the clock signal MCLK sentto the comparator 43 for a sufficiently long space can be determinedunequivocally in the case of the CAV system, whereas in the case of theCLV system, when a maximum value of an admissible number of revolutionsat the time when the spindle motor 2 is rotated in a free run is set,the length of time for this space can be used to determine the set data.

Therefore, when the control track area of the magneto-optical disc 1 isreproduced, the clock mark detection circuit 11 detects a space from theback end of a data area to a clock mark of the next segment and thus canspecify the position of the clock mark. With the use of the detectedclock mark, the PLL circuit 12 generates a servo clock SCLK synchronizedwith the clock mark, that is, synchronized with the rotational phase ofthe magneto-optical disc 1. In the case of the present embodiment, thePLL circuit 12 generates the servo clock SCLK by multiplying thefrequency of the clock mark by 325 times. In other words, one segment,which is a distance between the clock marks, includes 325 SCB.

Next, the specified position of the clock mark and the generated servoclock SCLK are used by the Bi-Phase decoder 13 for obtaining a period ofthe data area where the control data are recorded by emboss prepits andbit cell information of the Bi-Phase code to perform a Bi-Phasedemodulation. In the present embodiment, 3 SCB is set as 1 Bi-Phase bit,and 6 SCB is set as 1 control data bit. The control data after beingdemodulated by the Bi-Phase code are read out by the system controller21 and managed as information for determining the operating conditionsof the device for the magneto-optical disc 1.

The reproduction of the control data from this control track area can beperformed without a tracking control when the system controller 21 andthe servo processor 16 (servo control means) set the tracking controlfunction of the actuator driver 17 and the traverse driver 18 in anon-operating state. This is because the same control data to becompleted in 1 cycle are recorded in the plurality of tracks neighboringin the control track area. In the case of the present embodiment, thenumber of tracks where the control data are recorded amounts to severalhundreds of tracks, and the same control data are recorded over aphysical length of about 1 mm. Accordingly, the optical beam does notneed to trace the control tracks on the magneto-optical disc 1accurately any more, so that the control data can be read out in a shorttime only by performing a focus control.

In addition, the embodiment of the present invention referred to thecase in which the control track area is provided in the vicinity of theinner circumferential end, but it is also possible to provide thecontrol track area in the vicinity of the peripheral end and also bothin the vicinity of the inner circumferential end and in the vicinity ofthe peripheral end. In this alternative embodiment, depending on theposition of the control track area, the magneto-optical signalscorresponding to the user data can be recorded and reproduced from theinner circumference to the periphery of the rewritable track area orfrom the periphery to the inner circumference, and alternatively in bothdirections.

What is claimed is:
 1. An optical disc in which a plurality of concentric circular or spiral tracks are formed in a control track area where control data are recorded, in the vicinity of at least one selected from an inner circumferential end and a peripheral end, and in a rewritable area located outside the control track area for recording user data at least in one direction either from an inner circumference to a periphery or from the periphery to the inner circumference depending on the position of the control track area, the optical disc comprising a plurality of segments formed in each track, each segment including a clock area where a clock mark is arranged, a servo area where a pair of wobble marks displaced in both inner circumferential and peripheral directions from a center line of a track and separated by a predetermined distance in a circumferential direction, an address area where an address mark is arranged and a data area for recording the control data or the user data, wherein the clock mark, the wobble marks and the address mark are formed as prepits of an uneven shape, and, following the data area where the control data are recorded by the prepits of an uneven shape, a space of a predetermined length where the prepits do not exist is arranged for each segment in the control track area.
 2. The optical disc according to claim 1, wherein same control data are recorded in a plurality of tracks neighboring in the control track area.
 3. The optical disc according to claim 1, wherein the control data in the control track area are recorded by run-length-limited code.
 4. The optical disc according to claim 1, wherein the predetermined length of the space is a length exceeding a distance between the servo mark and a first prepit of the control data in the control track area.
 5. An optical disc device for driving an optical disc, in which a plurality of concentric circular or spiral tracks are formed in a control track area where control data are recorded, in the vicinity of at least one selected from an inner circumferential end and a peripheral end, and in a rewritable area located outside the control track area for recording user data at least in one direction either from an inner circumference to a periphery or from the periphery to the inner circumference depending on the position of the control track area, and a plurality of segments are formed in each track, each segment including a clock area where a clock mark is arranged, a servo area where a pair of wobble marks displaced in both inner circumferential and peripheral directions from a center line of a track and separated by a predetermined distance in a circumferential direction, an address area where an address mark is arranged and a data area for recording the control data or the user data, wherein the clock mark, the wobble marks and the address mark are formed as prepits of an uneven shape, and, following the data area where the control data are recorded by the prepits of an uneven shape, a space of a predetermined length where the prepits do not exist is arranged for each segment in the control track area, the optical disc device comprising reproduction means for reproducing pit signals corresponding to the prepits, clock mark detection means for detecting a pit signal following a distance of not less than a distance corresponding to the space length from the pit signals reproduced by the reproduction means as the clock mark, servo clock generating means for generating a servo clock synchronized with the clock mark detected by the clock mark detection means, and control data readout means for reading out the control data based on the servo clock.
 6. The optical disc device according to claim 5, further comprising tracking control means for controlling a center of an optical beam spot to be emitted on the optical disc to match a center line of a track, based on the results of the pair of wobble pits reproduced by the reproduction means, and servo control means for setting the tracking control means in a non-operating state at the time when the control data is read out by the control data readout means, wherein the same control data are recorded in a plurality of tracks neighboring in the control track area of the optical disc.
 7. The optical disc device according to claim 5, wherein the control data in the control track area of the optical disc are recorded by run-length-limited code, and the control data readout means comprises decoding means for decoding the control data recorded by the run-length-limited code. 